Generally, each joint of a multi-articulated industrial robot is conventionally provided with joint drive sources which include drive motors and reduction gears. The operation of the joint drive sources is controlled by a robot controller according to programs, stored in the robot controller, to cause relative displacements between movable elements about corresponding joint axes so that the accumulated relative displacement causes an end effector mounted on the wrist of the robot, i.e., the endmost movable element, to implement a desired operation.
In the described industrial robot, it often occurs at the job site that a drive motor or an associated reduction gear in a joint drive source malfunctions and must be replaced with a new motor or reduction gear.
In such a case, the defective operating element of the malfunctioning joint drive source, i.e., the drive motor or the reduction gear, is removed from the robot unit, and then a new drive motor or reduction gear is mounted on the robot unit to restore the joint drive source to its normal function.
In order to enable the industrial robot to perform any desired robot motion correctly, according to the program in the controller, after the defective drive motor or the defective reduction gear has been replaced with a new one, the geometrical positions of any two movable elements of the robot cooperatively joined together, for motions relative to each other, by the joint in which the drive motor or the reduction gear has been replaced with a new one must be unchanged from those before the replacement of the drive motor or the reduction gear, and the geometrical positions of the movable elements must be correctly taught to the entire system of the robot after completion of the replacement. The two movable elements of the robot are the robot body and the robot upper arm, the robot upper arm and the robot forearm, the robot forearm and the robot wrist, or the different parts of the robot wrist.
That is, the position before replacement, (original position) must be correctly restored and must be correctly taught to the robot.
Accordingly, original position adjustment, namely single-axis mastering, has conventionally been carried out.
The conventional single-axis mastering procedure applied to a multi-articulated industrial robot provided with a robot base 1, a robot body 2 capable of revolving about a joint axis (J1) relative to the robot base 1, a robot upper arm 3 capable of turning about a joint axis (J2) relative to the robot body, a robot forearm capable of turning about a joint axis (J3), supported on the extremity of the robot upper arm 3 relative to the robot upper arm 3, and a robot wrist 5 having three joint axes (J4 through J6) and three degrees of freedom of motion as shown in FIG. 2 will be described by way of example.
When a drive motor Mu of a drive source for driving the robot forearm 4 for rotating about the joint axis J3 malfunctions and it must be replaced with a normal one, the robot forearm 4 is rotated about the joint axis J3 relative to the robot upper arm 3 to bring a reference position P on the robot forearm 4, for original position setting, into contact with the tip of the arm of a dial indicator 9 fixedly held by a magnetic stand or the like on a measuring table 8.
In this state, the measurement indicated by the indicator hand of the dial indicator 9 is recorded, the geometrical position data U corresponding to the position of the joint axis J3 is read from a position detector incorporated in the drive motor Mu before replacement and the geometrical position data U is recorded.
The robot forearm 4 is then rotated about the joint axis J3 away from the dial indicator 9 relative to the robot upper arm 3, leaving the dial indicator 9 as it stands. Subsequently, the defective motor Mu is replaced with a new drive motor Mu. The robot forearm 4 is thereafter rotated to bring the reference position P into contact with the tip of the arm of the dial indicator 9 held on the measuring table 8 so that the indicator hand indicates the measurement indicated by the same before replacement. The geometrical position of the robot forearm 4 is thus guaranteed by the indication on the dial indicator 9. Then, the previously recorded geometrical position data U is given to the position detector (encoder) of the newly installed drive motor Mu via the robot controller, by operating the operating panel of the robot controller to complete the single-axis mastering for the joint axis J3. Thus, the same functions as before are restored and the industrial robot can perform desired robot operation.
As for the joint axis J2, when the drive motor or the reduction gear incorporated in the joint having the joint axis J2 malfunctions and must be replaced, a single-axis mastering procedure using the dial indicator 9 similar to the foregoing single-axis mastering procedure is carried out on the basis of geometrical position data W, as shown in FIG. 2.
Another conventional single-axis mastering procedure, which is different from the foregoing single-axis mastering procedure using the measuring table 8 and the dial indicator 9, uses alignment marks Q1 and Q2, as shown in FIG. 3, marked respectively on two members that move relative to each other on a joint, and uses the positions of the two members where the alignment marks Q1 and Q2 coincide with each other as the geometrical reference position of one of the two members relative to the other. When the drive motor or the reduction gear of a driving source for driving the joint malfunctions and must be replaced, position data corresponding to the geometrical reference position of the member, i.e., the position of the member in a state where the alignment marks Q1 and Q2 coincides with each other, is read from the position detector of the drive motor and the position data is recorded, the position of the member is adjusted after the replacement of the drive motor or the reduction gear with a normal one so that the alignment marks Q1 and Q2 coincide with each other to position the member at the geometrical reference position, and then the position data corresponding to the geometrical reference position is given by operating the control panel of the robot controller.
However, in carrying out the first single-axis mastering procedure employing the dial indicator 9 described with reference to FIG. 2, the dial indicator for positioning the robot member at the geometrical reference position before and after the replacement of the defective drive motor or the like must be kept in an absolutely stationary state during the replacement work for replacing the drive motor or the like.
If the dial indicator is moved inadvertently during the replacement of the drive motor or the like, the geometrical reference position is lost and single-axis mastering becomes impossible. Consequently, the single-axis mastering procedure must be executed for all the joint axes to restore the functions necessary for executing the desired programs taught to the robot unit, which takes a very long time.
Furthermore, often there is no place suitable for firmly placing the measuring table for fixedly holding the dial indicator 9 in the job site in which the industrial robot operates and, in such a case, a single-axis mastering procedure using the dial indicator cannot be carried out.
When carrying out the second single-axis mastering procedure using the alignment marks Q1 and Q2 shown in FIG. 3, the coincidence of the alignment marks Q1 and Q2 is confirmed visually by an operator. Therefore, it often occurs that the geometrical position determined after the replacement of the defective drive motor or the defective reduction gear of the joint drive source deviates minutely from the geometrical position before the replacement of the defective drive motor or the defective reduction gear. Accordingly, a teaching operation, which is a time-consuming operation, must be performed to correct the program in the controller after the replacement work.